Astrocytes should be an apostrophe differentiation and function are investigated at protein and gene levels. To identify astrocyte-specific markers, plasma membrane, nuclear, and nuclear matrix proteins were resolved by two-dimensional electrophoresis and compared to those in neurons, glioma C6 cells, and kidney fibroblasts. Two abundant membrane proteins were identified, purified to homogeneity, and will be characterized by means of antibodies. To characterize evolution of brain gliomas, we examined expression of glial fibrillary acidic protein (GFAP), an astrocyte marker, in normal and transformed human astrocytes. In these cells GFAP appeared to be regulated by post-translational modification and its assembly seemed to be controlled by GTP. GFAP in malignant gliomas and fetal astrocytes were similarly charged, while in benign glioma cells it was more electronegative. Brain glutamine synthetase, a key enzyme in nitrogen metabolism and localized in astrocytes, is regulated developmentally and hormonally. Five cDNA clones were identified in a mouse brain library that hybridized with a cloned hamster glutamine synthetase gene. We will use these clones to study the transcriptional regulation of the glutamine synthetase gene.